1. Technical Field
The invention relates to parallel or homogeneous distributed databases and more particularly to supporting of distributed update requests within a transaction on a parallel database.
2. Background
A distributed database system is one implemented over a communication network linking a plurality of computers. The database itself is partitioned among the individual computers. A database request from an application program running on one computer can be sent to one or more remote computers over the network. To handle such a request a coordinator running on a computer (either the computer where the application program is executing or a remote computer which exclusively handles coordination) decides whether the transaction owning the request is to be committed or rolled back. A true distributed request is permitted to span multiple computers. Its operation is transparent to the user and to the application program. For example, the request may involve the virtual union of partitions on mutually remote computers.
Throughput in a distributed database system should be better than in a nondistributed database system because requests from a transaction can be divided among appropriate remote computers or span partitions where more than one partition is appropriate. The handling of requests in parallel is readily handled as long as no modification of the database is required. A request which involves any modification of the records of the database has forced serialization (i.e. completion) of requests in order to allow for distribution of the request without compromising rollback of the transaction if later required.
A distributed transaction (also called a distributed unit of work) may include several distributed update requests. Requiring serialization of all operations from the requests compromises the principle of executing the transaction in parallel. Throughput then falls below possible levels.